A molecule must have a chiral center with four different substituents to be considered chiral. If the central carbon has two identical groups, the molecule is achiral.
A molecule is considered chiral if it has a non-superimposable mirror image, which generally requires the presence of a chiral center. A chiral center is typically a carbon atom bonded to four different groups. If a molecule has a plane of symmetry or superimposable mirror images, it is achiral.
- Option (A): 2-Chlorobutane is a chiral molecule. The second carbon is bonded to four different groups, making it a chiral center.
- Option (B): 2,3-Dihydroxy propanal is a chiral molecule because both the second and third carbon atoms are each attached to four different groups, which makes the molecule chiral.
- Option (C): 2-Bromo propionic acid is also chiral because the central carbon (C-2) has four different substituents, making it a chiral center.
- Option (D): Butan-2-ol is a chiral molecule. The second carbon is attached to four different groups, so it is a chiral center.
- Option (E): 2-Bromo-2-methoxypropane is not chiral. The central carbon (C-2) is attached to two identical groups (a bromine and a methoxy group), making it a symmetrical center. As a result, this molecule has a plane of symmetry and is achiral.
Thus, the correct answer is (E) 2-Bromo-2-methoxypropane, which is not chiral.
are isomeric compounds. 
are functional group isomers.